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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Optical coherent transient processes in thin semiconductor quantum wires

Pranay K. Sen

Published Sep 25, 2001• 0 citations
Publisher

Abstract

The paper discusses the analytical investigation of the occurrence of coherent optical transient processes such as dynamic Stark effect and free induction decay in direct-gap semiconductor quantum wires with thickness and width smaller than the bulk Wannier-Mott exciton Bohr radius. The role of a moderately strong magnetic field has been critically evaluated in the occurrence of the transient processes. The analysis is based upon the time dependent perturbation treatment of the coherent radiation-semiconductor interaction model under near band gap resonant excitation regime. The excitation intensity is kept below the Mott transition regime. Numerical estimates made for a GaAs/AlGaAs quantum wire irradiated by femtosecond pulse Ti:Sapphire laser establishes that the Stark shift, Stark broadening as well as free induction decay are all considerably influenced by the magnetic field. Moreover, the wire width also affects Stark splittings.

DOI
10.1117/12.441284

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The paper discusses the analytical investigation of the occurrence of coherent optical transient processes such as dynamic Stark effect and free induction decay in direct-gap semiconductor quantum wires with thickness and width smaller than the bulk Wannier-Mott exciton Bohr radius. The role of a moderately strong magnetic field has been critically evaluated in the occurrence of the transient processes. The analysis is based upon the time dependent perturbation treatment of the coherent radiation-semiconductor interaction model under near band gap resonant excitation regime. The excitation intensity is kept below the Mott transition regime. Numerical estimates made for a GaAs/AlGaAs quantum wire irradiated by femtosecond pulse Ti:Sapphire laser establishes that the Stark shift, Stark broadening as well as free induction decay are all considerably influenced by the magnetic field. Moreover, the wire width also affects Stark splittings.
We have proposed a simplified theoretical model to examine the optical nutation in one-dimensional semiconductor quantum wires. We explored the role of excitons, biexcitons, and the effect of confinement in enhancing transient optical processes in such semiconductor nanostructures. We apply the time dependent perturbation technique to the coherent radiation-semiconductor interaction for a three-level system in the near band gap resonant excitation regime. We have incorporated the relaxation and dephasing mechanisms phenomenologically. The induced polarization is calculated theoretically and the role of biexciton density on the polarization is analyzed. Numerical estimations of refractive and absorptive optical nutation have been made for a GaAs∕AlxGa1−xAs quantum wire duly shined by femtosecond pulse Ti: sapphire laser. Our results agree qualitatively with available experimental observations.
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Using a coherent radiation-semiconductor interaction model based upon the time dependent perturbation technique, the occurrence of optical nutation has been analytically investigated in direct-gap semiconductors such as GaAs, GaSb, InAs, and Hg1-xCdxTe, duly irradiated by near resonant laser beams. The present approach is much more simplified and straightforward than the conventional Maxwell-Bloch approach used so far for the study of coherent optical transient effects in molecular and atomic systems. The dispersion and absorption expressed in terms of the real and imaginary parts of the crystal optical susceptibility\chi_{r}and\chi_{i}exhibit temporally damped ringing behavior of Neumann and Bessel types, respectively. These processes have been identified as dispersive and absorptive optical nutation. The theory is developed for arbitrary laser intensity in presence of damping due to nonoptical processes. To understand the mechanisms of dispersive and absorptive optical nutation, we have restricted only to low-power resonant band-to-band transitions neglecting excitonic and damping effects. While studying analytically the transient behavior of\chi_{r}and\chi_{i}for a given pump field strength, it is noticed that the absorptive component exhibit remarkable qualitative agreement with the experimental observations of optical nutation in13CH3F.
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